The present invention relates to a casting apparatus, and more particularly to a casting apparatus for cold-chamber die-casting machines which is capable of feeding molten metal safely into an injection sleeve or chamber and of producing high-quality castings, and which is small in size.
Casting apparatus have widely been used for obtaining a large quantity of desired cast products by pouring molten metal into a die cavity of given shape and allowing the poured molten metal to be solidified in the die cavity. Casting apparatus can roughly be classified as hot-chamber and cold-chamber casting apparatus.
One conventional cold-chamber die-casting machine is illustrated in FIG. 1 of the accompanying drawings. The illustrated cold-chamber die-casting machine includes a firmly fixed frame 2 on a floor, on which a fixed die plate 4 is securely mounted, with a fixed die 6 being secured to the fixed die plate 4. A movable die plate 8 is mounted on the frame 2 in confronting relation to the fixed die plate 4. The movable die plate 8 can be moved by a die clamping mechanism through a link mechanism (not shown). A movable die 10 is mounted on the movable die plate 8. The fixed die plate 4 and a link housing (not shown) constituting the die clamping mechanism are mounted on four tie bars 11 (only two shown in FIG. 1) and fastened thereto by tie bar nuts 12.
The movable die plate 8 is guided by the tie bars 11 while moving horizontally on the frame 2 toward and away from the fixed die plate 4. A recess 14 is defined centrally in an outer side surface of the fixed die plate. An injection sleeve or chamber 16 extends horizontally through the fixed die plate 4 and the fixed die 6 at a lower portion of the recess 14. The injection sleeve 16 has an inner open end lying flush with the inner side surface of the fixed die 6. A substantially half length of the injection sleeve 16 extends out of the fixed die plate 4. The portion of the injection sleeve 16 which extends out of the fixed die plate 4 has a relatively large pouring slot 17 defined in an upper wall thereof.
A runner 20 for supplying molten metal into a die cavity 18 defined by and between the fixed die 6 and the movable die 10 is defined in the injection sleeve 16 within the fixed die 6 and has a length hl from the interface or boundary between the movable die 10 and the fixed die 6 as they are held together. A frame 19 is affixed to the fixed die plate 4 and supports an injection cylinder 22 in confronting relation to the injection sleeve 16. The injection cylinder 22 houses a piston 24 disposed slidably therein. The piston 24 is coupled to one end of a piston rod 25, the other end thereof being connected through a coupling 26 to a rod 28. The rod 28 is coupled at its distal end to an injection plunger tip 30 that is slidably disposed in the injection sleeve 16. A crucible furnace 34 for containing molten metal 32 and keeping the same at a prescribed temperature is disposed adjacent to the die-casting machine. The molten metal 32 contained in the crucible furnace 34 is scooped by a ladle 36 and poured from the ladle 36 through the pouring slot 17 into the injection sleeve 16. Thereafter, the injection cylinder 22 is actuated to cause the injection plunger tip 30 to force the poured molten metal from the injection sleeve 16 through the runner 20 into the die cavity 18.
The conventional die-casting machine shown in FIG. 1 has proved disadvantageous for the following reasons: The relatively large pouring slot 17 is dangerous in that the operator's hand may inadvertently enter the pouring slot 17 and that the poured molten metal may be spouted from or overflow the pouring slot 17, or be scattered around from the pouring slot 17. When the molten metal is to be poured into the injection sleeve 16, the molten metal 32 is first scooped from the crucible furnace 34 by the ladle 36 and then supplied from the ladle 36 through the pouring slot 17 into the injection sleeve 16. Therefore, the molten metal 32 remains exposed to air and gets oxidized while it is being transported from the crucible furnace 34 to the injection sleeve 16, with the result that the injection sleeve 16 cannot be supplied with pure molten metal. At the time the molten metal is injected from the injection sleeve 16 into the die cavity 18, the surface of the molten metal 32 within the injection sleeve 16 must be lower than the pouring slot 17. In practice, the charging efficiency of the injection sleeve 16 for the molten metal is 40 through 50% or less in terms of the ratio of the volume of the poured molten metal to the volume of the injection sleeve 16.
The charging efficiency of the conventional die-casting machine has been increased by increasing the length to the stroke (hereinafter referred to as an "injection stroke") which the injection plunger tip 30 has to move in the injection sleeve 16. The injection stroke thus increased has been 2 to 2.5 times larger than an injection stroke which is originally required, resulting in a large-size and costly hydraulic device needed to operate the injection plunger tip 30.
The recess 14 must be provided for the ladle 36 to be operated without physical interference with the fixed die plate 4. The recess 14 however reduces the mechanical strength of the fixed die plate 4.
The molten metal in the injection sleeve 16 is injected by the injection plunger tip 30 when the charging efficiency of the injection sleeve 16 for the molten metal therein is in the range of from 40 to 50%. Upon injection of the molten metal, the molten metal near the plunger tip 30 is caused thereby to swirl up, trapping air as indicated at A in FIG. 2. This results in blowholes or cavities in the produced die casting.
Where the die cavity defined by the fixed and movable dies is small and so is the volume of a resulting die casting, the injection sleeve 16 may be short since the amount of molten metal 32 to be transported by the ladle 36 needs to be small. However, inasmuch as the fixed die plate 4 is significantly thick even with the recess 14 defined therein and the pouring slot 17 is positionally limited in order to achieve easy maneuvering of the ladle 36, the injection sleeve 16 is inevitably longer than necessary. Before the molten metal 32 is introduced into the die cavity 18, an amount of molten metal 32 which is greater than required to fill up the relatively small die cavity 18 must be charged into the relatively long injection sleeve 16. It has been customary to reduce the excess molten metal that remains in the injection sleeve 16 after the die cavity 18 has been filled, by increasing the length of the runner 20 of the movable die 10 up to h2 as shown in FIG. 3, thereby to shorten the effective length of the injection sleeve 16.
Increasing the length of the runner 20 has however resulted in a low yield for die castings and an increased cost of manufacture.
The present invention has been made in an effort to overcome the aforesaid problems of the conventional casting apparatus.